Outline

Objective: The purpose of the study is to examine the anatomical relationship between the vertebral artery (VA), the cervical pedicle, and their surrounding structures including the incidence of irregularities. The second objective is to provide data delineating a “safety zone” and its application in the use of transpedicular instrumentation.

Methods: 127 patients that received CTA of the neck were enrolled in the study. On axial CTAs bilateral measurements were performed between C2 and C7. Measurements included: medial and lateral pedicle border to VA (MPVA and LPVA, respectively), pedicle diameter (PD), sagittal and coronal diameter of the VA (DVAS and DVAC, respectively), and sagittal and coronal diameter of the transverse foramen (DTFS and DTFC, respectively). The cross sections of the VA and the transverse foramen were measured to determine the occupation ratio (OR) of the VA. Finally, a “safety zone” was determined by measuring the distance that the VA, in theory, can be displaced laterally without being harmed by a misplaced pedicle screw. Level of entry point of the VA as well as irregularities of the VA and the cervical pedicle were recorded.

Results: The mean VA diameter was 3.24 mm right and 3.55 mm on the left side. 12.6% of patients presented with hypoplastic arteries. A dominance of the left VA was seen in 69.3% of the patients. Mean PD increased from 4.9 mm to 6.5 mm between C3 and C7. Significant differences were seen in PD between males and females (p<0.0001). C2 was found to be different with regard to pedicle diameter with a mean of 5.6 mm. Mean LPVA increased from 1.1 mm to 6.5 mm from C2 to C7. Entry of the VA at C6 was seen in 78%. The OR of the VA was found to be the greatest in C4 and C7 (37.1 and 74.2%, respectively). The study shows that there appears to be a “safety zone” between the cervical pedicle and the VA. In 23.6% of the patients we detected an irregular pathway of the VA, with the highest incidence of irregularities found in C2.

Conclusions: CTA is a valuable tool that can help in determining a “safety zone” between the VA and the lateral pedicle border as well as irregular VA pathways. The clinical significance of the abundant space besides the lateral pedicle (“safety zone”) and how this information should be used needs to be further determined. Because of the high percentage of irregular VA pathways we highly recommend performing and reviewing CTA studies of the neck before instrumenting the cervical spine.